Art of coloring mineral matter



Patented Aug. 1933 UNITED STATES PATEN OFFICE;

ART or conoanve MINERAL MATTER poration of Ohio No Drawing.

Application February a, 19cc Serial No. 425,722

3 Claims. (01. 91-70) My invention is related to processes of coloringmineral material such as granular, natural deposits of various kinds.Slate or other materials having a slaty cleavage are-generally pre- 5ferred because they break up into granules of a shape believed to besuperior for surfacing. Slate is not, however, the only materialsuitable for use; and indeed so far as the coloring process itself isconcerned, since the mineral granm ules in the process hereinafter-to bereferredto, are essentially merely a vehicle or support for thesuperimposed color coating, I am mot aware of any mineral substancewhich is not suitable for coloring providing only it will withstand aroasting treatment within the; degrees of time.

and temperature control of which the process is susceptible.

The general process referred to is set forth in the application of HarryC. Fisher, Ser. No.

$26,829, filed April 29, 1925, which teaches generally the coating ofmineral granules with'a soluble silicate such as a silicate of soda orpotassium, and a pigmenting substance, and afterwards dehydrating thecoating on the granules tofrender the silicate substantially insoluble,hard, permanent and weather resisting.-

Patent No. 1,572,425, issued Feb. 9, 1926, to

The general object of my invention is to produce a coating substancewhich may be applied to granule surfaces all in one operation, whicheffects a better utilization of the pigmenting material, and which givesin the final product better colors and a degree of color controlirrespective of the amount of pigment used. In other words, one objectof my invention is the more effective use of the same amount of pigment.

These and other objects of my invention which may be set forthhereinafter or which will be apparent to one skilled in the art uponreading these specifications, I accomplish by that certain process ofwhich I shall now describe a preferred embodiment, it being understoodthat modifications may be made in my process without departing from thespirit of my invention. Heretofore, it has been the practice merely tomix the pigmenting material with the silicate of soda solution (and suchamounts of water as may be required) and then to impose this coatingsubstance upon the granule surface, or to follow the procedure of PatentNo. 1,572,425 hereinabove referred to. It has also been suggested toproduce a silicate which per se is colored just as glass might becolored, prior to the operations necessary to put the said silicate intowater solution. All of these processes are feasible and givecommercially satisfactory col-' ors; but Ihave discovered not only thatI can greatly improve the color but also control the depth thereof to avery considerable extent by effecting-a more intimate admixture and adispersion of the pigmenting material in the silicate before coating thegranules therewith; and the way in-which I accomplish this, briefly, isby grinding together the soluble silicate and the coloring pigment withor without the addition of water. I have found satisfactory for thispurpose the use of a pebble or ball mill, and so in practicing myinvention I introduce the silicate of soda, water and coloring pigmentinto the mill and grind them together. By this method the( pigment isusually reduced considerably in fineness,-the silicate is ground intoeach particle and there is efiected an extremely fine and uniformdispersion of the pigment in the silicate body. Into each particle ofcoloring pigment a certain definite amount of silicate of soda isground. As the particles of pigment become fully impregnated, they breakdown more rapidly; andthe absorption of silicate of soda becomes greaterin proportion. The result of this grinding together of the-silicate andthe pigment is the formation of what may be termed a colored silicate ofgreat intensityof color and relatively great permanence in the sensethat there'is very little tendency for the coloring matter to settle outupon standing. In this way not only is a more homogeneous and completedispersion of the color effected throughout the body of the silicate,but when the color coating material is applied to the granules, thecolor distribution is better on the granule surfaces; and I have 105found that by this process I secure in the finished product greatlyintensified colors. I do-not wish to limit myself by theories as to whythis is so. However, I believe that color distribution is an importantfactor in the increased 'vidness 110 which I obtain. Again however,where he pig- I recognize that grinding the pigment with the silicatemay more effectively protect the pigment particles from the roastingtreatment as depending on the intensity of the hue desired.

However, the order of adding the material to the ball mill may be variedwith but little change, and I do not wish to limit myself in thisrespect. In some cases I have found it better to grind the silicate ofsoda and pigment together and later to thin the mixture with water;while in other cases it is preferable to add all of the materials at onetime to the mill. Similarly I do not wish to limit myself to the time ofgrinding. As has been suggested; I have found that the time of grindingper se will vary the hue of the resultant product in many cases, thusgiving me with the same materials in the same proportions, a colorcontrol not heretofore discovered. Up to a certain limit, the color ofthe pigments used is intensified the longer the grinding is continued.Apparently there is a point. at which the pigment becomes so fine and isso intimately admixed with the silicate that further mechanical grindingdoes not produce markedcolor intensification; but the time of grindingwill vary with the pigments used and the size of pigment particles.Having arrived at the best time of grinding to produce a desired hue forany given formula, it is my practice then to adhere rigidly to-this timefor this formula in commercial practice.

. I have not set forth herein any formula. It is preferable to use, asset forth in the copending application hereinabove referred to, asilicate of soda having a high SiOz content in relation to the NazOcontent. I may usethe formulae specifically set forth in the saidcopending application, or I may use other formula: and other pigmentingsubstances as may appear desirable to produce new colors.

ment used is one, the color of which is likely to be affected by heat inthe roasting treatment,

Having ground the silicate of soda into the pigment and having producedthereby a syrupy mixture, I next add the desired amopnt of this mixtureto the slate granules in an agitator, and after a thorough mixing sothat each particular granule is well colored, I then follow this with arapid heat treatment to dehydrate the silicate and render it weatherresistant, as described in the said copending application or in PatentsNos. 1,572,425 or 1,631,628. I may, of course, employ other treatmentsincluding the one set forth in my copending application Serial No.425,723, filed Feb. 3, 1930; my present invention'is concerned with thepreparation of the color coating. I I

It will be understood that my invention is not limited to the use of anyparticular vehicle or any particular pigmenting substance, and that Imay for example, add to a suitable vehicle, materials other thanpigments, such as glass forming materials, fluxes ,and the like, or thatI may use more than one/pigment or combinations of pigments and othersubstances.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. A process of coloring mineral granules such as slate, which comprisesgrinding together a pigmenting substance and a solution of silicate ofsoda, imposing the material thus formed upon the mineral granules, andheat-treating the mineral granules with agitation, to the extent offorming thereon a weatherproof coating.

2. A process of coloring mineral granules such as slate,,which comprisesgrinding together a pigmenting substance and a soluble silicate solutionto the extent of distributing said substance in finely divided formthroughout said solution, afterward imposing the material thus formedupon the mineral granules, and roasting the mineral granules withagitation.

3. A process of coloring mineral granules such as slate, which comprisesgrinding together a HORATIO L. SMALL.

